An amyloid β is a peptide consisting of 40 or 42 amino acids and is generated from an amyloid β precursor protein (APP) cleaved by β-selectase and γ-selectase. The amyloid β with 40 amino acids is referred to as amyloid β (1-40) and the amyloid β with 42 amino acids is referred to as amyloid β (1-42). The amino acid sequences of the amyloid β (1-40) and amyloid β (1-42) are as follows.
Amyloid β (1-40) (Amino acid sequence No. 5)DAEFRHDSGYEVHHQKLVFFAEDVGSNKGAIIGLMVGGVV Amyloid β (1-42) (Amino acid sequence No. 6)DAEFRHDSGYEVHHQKLVFFAEDVGSNKGAIIGLMVGGVVIA
Of these amyloids β, the amyloid β (1-40) is reported to be a peptide cleaved via a common metabolic pathway and to have weak toxicity. On the other hand, the amyloid β (1-42) is said to be insoluble, have strong toxicity, easily agglomerate into a fibrous form, and be accumulated in the brain and cause Alzheimer's disease.
Therefore, assaying each amyloid β peptide is very important in diagnosing Alzheimer's disease and investigating the mechanism of Alzheimer's disease occurrence.
Heretofore, an amyloid β antibody has been used for assaying an amyloid β (for example, Patent Document 1). However, since the amyloid β antibody described in the Patent Document 1 has an epitope in the 3-8 site of the amino acid sequence of the amyloid β, an amyloid β assay kit using this antibody detects amyloid β precursor proteins (APP), as well as amyloid β (1-40) and amyloid β (1-42) possessing the entire length of amino acid sequence. A presently commercially available amyloid β antibody (“6E10” manufactured by Signet Laboratories, Inc.) also recognizes APP.
In addition, a method of suppressing accumulation of amyloid β in the brain in order to prevent Alzheimer's disease has been investigated. However, since the presently known amyloid β antibodies react not only with an amyloid β, but also APP in normal cells, these antibodies have high possibility of causing side reaction such as inflammation and, therefore, have not been clinically applied.    Patent Document 1: WO 1994/017197 pamphlet